1. Field of the Invention
The invention generally relates to an apparatus and a method for processing semiconductor substrates. More particularly, the invention relates to a method and apparatus for high density plasma chemical vapor deposition of films onto substrates.
2. Background of the Related Art
Plasma tools used for semiconductor processes, such as chemical vapor deposition (CVD), etching, reactive ion etching and so forth, typically employ either inductive coupling or capacitive coupling of a plasma generator to the processing chamber to strike and maintain a plasma. One advantage of inductively coupled plasmas over capacitively coupled plasmas is that the inductively coupled plasma is generated with a much smaller bias voltage on the substrate, reducing the likelihood of damage to the substrate. In addition, inductively coupled plasmas have a higher ion density thereby providing higher deposition rates and mean free paths, while operating at a much lower pressure than capacitively coupled plasmas. These advantages allow in situ sputtering and/or deposition during processing.
More recently, high density plasma (HDP) CVD processes have been used to provide a combination of chemical reactions and physical sputtering. HDP-CVD processes promote the disassociation of the reactant gases by the application of radio frequency (RF) energy to the reaction zone proximate the substrate surface, thereby creating a plasma of highly reactive ionic species. The high reactivity of the released ionic species reduces the energy required for a chemical reaction to take place, thus lowering the required temperature for these processes.
The goal in most HDP-CVD processes is to deposit a film of uniform thickness across the surface of a substrate, while also providing good gap fill between lines and other features formed on the substrate. Deposition uniformity and gap fill are very sensitive to the plasma generator source configuration, source radio frequency generator power, bias radio frequency generator power, process gas flow changes and process gas nozzle design, including symmetry in distribution of nozzles, the number of nozzles, the height of the nozzles disposed above the substrate during processing and the lateral position of the nozzles relative to the substrate deposition surface. These variables change as processes performed within the tool change and as process gases change.
FIG. 1 is a cross sectional view of a HDP-CVD chamber useful for depositing a variety of films on a substrate. An example of a HDP-CVD chamber is the Ultima HDP-CVD system available from Applied Materials, Inc. of Santa Clara, Calif. Generally, the HDP-CVD chamber 100 comprises a chamber enclosure 102, a substrate support member 104, a gas inlet 106, a gas exhaust 108 and a dual coil plasma generator 110. The chamber enclosure 102 is typically mounted on a system platform or monolith, and an upper lid 112 encloses an upper portion of the chamber enclosure 102. A dome 114, typically made of a ceramic such as aluminum oxide (Al.sub.2 O.sub.3), is disposed on the lid 112. The dual coil plasma generator 110 typically comprises a first and a second coil, 116, 118, and a first and a second RF power source, 120, 122, electrically connected to the first and second coils, 116, 118, respectively. To provide the high density plasma, the first coil 116 is disposed around the dome 114 while the second coil 118 is disposed above the dome 114. The gas inlet 106 typically comprises a plurality of gas nozzles 124 disposed around an interior circumference of the chamber in a region above the substrate support member. Typically, the gas nozzles 124 extend from the interior surface of the chamber to a distance above a substrate positioned on the substrate support member 104 to provide a uniform distribution of the processing gases to the substrate during processing. The gas exhaust 108 comprises a gas outlet 126 and a pump 128 to evacuate the chamber and control the pressure within the chamber during processing. During the deposition process, process gases are introduced through the gas inlet 106 and a plasma of the processing gases is generated within the chamber to effectuate chemical vapor deposition onto the substrate. The deposition typically occurs on all the surfaces exposed to the processing gases, including the interior surfaces of the chamber, such as the dome 114, because the processing gases are introduced at the same flow rate through gas nozzles 124 that have the same lengths to provide a uniform gas distribution within the chamber.
High density plasma (HDP) processes have become important processes used in the fabrication of integrated circuits. HDP processes can be used advantageously to deposit thin films or etch films on a substrate to form integrated circuits. As with other deposition and etch processes, an important consideration is the level of contaminants present in the processing environment. In HDP processes, this is important because the high density plasma typically creates higher temperatures within the process chamber. As the temperature in the process chamber increases, the likelihood that undesirable mobile ion and metal contaminants will be driven out of chamber components increases. Therefore, particle counts within the HDP process environment may be unfavorably high.
Particle contamination within the chamber is controlled by periodically cleaning the chamber using a plasma of cleaning gases, typically fluorinated compounds. Cleaning gases are selected based on their ability to bind the precursor gases and the deposition material which has formed on the chamber components in order to form stable products which can be exhausted from the chamber, thereby cleaning the process environment. In a high density plasma reactor, most cleaning gases containing fluorine (i.e., NF.sub.3, CF.sub.4, and C.sub.2 F.sub.6) are highly dissociated and can readily bind the deposition material forming a stable product which can be exhausted from the chamber.
Typically, before the deposition process, the interior surfaces of the chamber are cleaned and then coated with a seasoning coat to protect these surfaces from the processing gases. The seasoning coat is typically formed by depositing the deposition material onto the surfaces within the chamber before a substrate is introduced into the chamber for processing. This step is typically carried out by depositing a film to coat the interior surfaces forming the processing region in accordance with the deposition process recipe.
As one process example, silane gas can be introduced into the chamber and oxidized to deposit a layer of silicon dioxide according to the following equation: EQU siH.sub.4 +O.sub.2 .fwdarw.SiO.sub.2 +2H.sub.2 EQUATION I
In a 200mm substrate application, a deposition process is typically carried out using a source RF power of about 4500W and a bias RF power of about 2500W. The season step prior to deposition is carried out using a source RF of about 4500W and a bias RF of about 1600W. In a 300 mm substrate application, the deposition process is typically carried out using source RF of about 10,125W and a bias RF of about 5625W. The season step prior to deposition is carried out using a source RF of about 10,125W power and a bias RF power of about 3600W.
After processing a number of substrates, the seasoning coat is removed or cleaned from the interior surfaces of the chamber along with any material deposited on the seasoning coat, and a fresh seasoning coat is applied to the interior surfaces of the chamber to provide a clean, consistent environment for processing the next batch of substrates.
One problem encountered with deposition using the HDP-CVD chamber is that when the chamber is used to deposit a fluorine based film, such as fluorosilica glass (FSG), the fluorine in the plasma diffuses through the seasoning coat and attacks the ceramic (Al.sub.2 O.sub.3) dome. The fluorine atoms that reach the ceramic dome react with the ceramic to form Al.sub.2 O.sub.x F.sub.y (where x and y are integers) on the surface of the dome. It has been determined with Secondary Ion Mass Spectroscopy (SIMS) analysis that dome blackening and process drifts are caused by Al.sub.2 O.sub.x F.sub.y formation on the dome. The Al.sub.2 O.sub.x F.sub.y formation on the dome alters the electrical properties of the dome material and causes process drifts in the deposition uniformity, the deposition rate, the fluorine concentration and the sputter uniformity in the chamber. Because of the process drifts, non-uniform processing occurs across the surface of a substrate and from one substrate to another substrate.
As an attempt to solve the process drift problem and to prevent diffusion of the fluorine atoms through the seasoning coat, a thick seasoning coat (&gt;1000 .ANG.) is deposited prior to processing of each substrate. The thick seasoning coat prolongs the time required for the fluorine atoms to diffuse through the seasoning coat and reach the dome. However, when the process time is sufficiently long, the fluorine atoms are still able to diffuse through the seasoning coat to form Al.sub.2 O.sub.x F.sub.y on dome and cause process drifts. Furthermore, an excess amount of time is spent depositing and removing the thick seasoning coats. The seasoning coat must be removed after a number of substrates have been processed to ensure that the fluorine atoms do not diffuse through the seasoning coat and form Al.sub.2 O.sub.x F.sub.y on the dome, and a fresh seasoning coat must be deposited before the next batch of substrates are processed. The excess time spent in depositing and removing the thick seasoning coat is another major disadvantage because the throughput of the system is reduced.
Another problem associated with deposition of doped silicon glass using a HDP-CVD chamber is that the current gas distribution system does not provide uniform dopant delivery across the surface of the substrate, resulting in a deposited doped silicon glass film having material property differences across the surface of the substrate. In general, uniformity in processing is desired to maintain product quality.
Therefore, there exists a need for an apparatus and a method of depositing a film on a substrate that eliminates the contamination of the dome by fluorine and other gases and the resulting problems of process drifts. It would be desirable for the apparatus and the method to provide an increased throughput by reducing the time required for forming and removing the seasoning coat on the interior surface of the dome. It would be further desirable for the apparatus and the method to provide uniform dopant delivery across the surface of the substrate to achieve uniformly doped silicon glass films.